Ink drop writing apparatus



Sept. 2,

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DROP DETECVOR PHASE. INVENTORS CONTROL ROBE/2T1 KEHR ORG/T /-/A//-?Y A. DAHL BY AJ QLFJJI United States Patent 3,465,351 INK DROP WRITING APPARATUS Robert I. Keur, Niles, and Henry A. Dahl, Mount Prospect, Ill., assignors to A. B. Dick Company, Chicago, Ill., a corporation of Illinois Filed Mar. 13, 1968, Ser. No. 712,808 Int. Cl. Gold 15/18 U.S. Cl. 34675 9 Claims ABSTRACT OF THE DISCLOSURE In an apparatus of the type wherein ink under pressure is applied to a nozzle which is vibrated, and the ink emitted by the nozzle thereafter breaks down into ink drops which are charged in a charging tunnel in response to a video signal, means are provided, in accordance with this invention, for controlling the phase of the vibration of the nozzle relative to the video charging signal to insure correct phasing of the ink drops emitted by the nozzle and as a result proper charging of the ink drops by the video signals is made to occur. All the drops, which pass out of the charging tunnel strike the drop charge detector. The drop charge detector provides an output from which an indication of the phasing of the ink drops is derived.

BACKGROUND OF THE INVENTION An ink drop writing apparatus has been developed wherein ink is applied under pressure to a nozzle. The nozzle is vibrated in response to a synchronizing signal which is also used for synchronizing video signals. The vibrated nozzle causes an ink jet, which is emitted therefrom, to break up into uniform drops at a distance away from the tip of the nozzle. The rate of such drop formation is determined by the vibration rate. A means for charging each drop is provided at the location at which the ink stream begins'to break into drops. This means usually is a conductive tube or cylinder. Video signals are applied between the nozzle and the cylinder in response to which a drop assumes a charge determined by the amplitude of the video signal at the time that the drop breaks away from the jet stream.

The drop thereafter passes through a fixed electric field, as a result of which it is deflected by an amount determined by the amplitude of the charge on the drop. At the boundary of the electric field there is positioned a writing medium upon which the drop falls. Since the deflection of the drop is determined by the charge on the drop, the arrangement enables one to write information with the ink which is carried by the video signal.

As previously stated, at the time that a drop separates from the fluid stream, the drops are charged by electrostatic induction. If the field established by the video signal is maintained while the drop separates, the drop will carry a charge determined by this video signal. Obviously, if the video signal is in the process of rising or falling or is not present at the time the drops separate, the charge on the drop will not be that of the video signal. In order to place specific charges on given drops, one must know when drop separation is occurring or the phasing of the drop formation relative to the video signal. In the absence of control over drop separation time, because of unpredictable phase changes in the ink Patented Sept. 2, 1969 drop formation, the uniformity and the fidelity of the printing are affected adversely.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is to enable detection and correction of incorrect ink drop phasing.

It is another object of this invention to afford an arrangement for improving the unformity and the fidelity of printing using an ink drop printing system.

Still another object of the present invention is the provision of apparatus which eliminates the problems created by incorrect time of drop formation.

This invention comprises an arrangement for providing test video signals for charging ink drops and detecting whether the ink drops are properly charged by placing an ink drop detector at a location to which they should be deflected if properly charged. If the ink drop detector does not detect ink drops, the phase of the formation of the ink drops is shifted to correct for this.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a block schematic drawing of a prior art ink drop writing system.

FIGURE 2 is a schematic drawing of an arrangement of an ink drop printing system with which this invention may be employed.

FIGURE 3 is an enlarged view illustrating, in accordance with this invention, ink drop formation in an ink drop printing system;

FIGURE 4 schematically illustrates another arrangement for correcting ink drop phasing; and

FIGURE 5 is a schematic drawing of an ink drop phase correcting circuit in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGURE 1 is a schematic drawing of the presently known arrangement which is shown to afford a better understanding of the invention. An ink reservoir 10 provides ink under pressure to tubing 12 which is flexible. An electromechanical transducer 14 is usually placed adjacent to or around the tubing. The transducer is driven in response to signals from a source 16. The transducer serves to vibrate and/or compress the tubing 12 in the region of the nozzle 18. This results in an ink jet 20 being emitted which at a short distance downstream breaks up into drops 22 which are formed at a rate determined by the frequency of the vibration. In the region where the stream 20 breaks down into drops, a charging tunnel 24 is provided. This comprises a conductive cylinder to which video signals from a video signal source 26 are applied. The video signals establish a field within the charging tunnel so that the ink drops which are formed therein assume a charge determined by the amplitude of the video signal present at the time the drop separates from the ink jet 20.

Downstream of the charging tunnel there are usually placed a pair of electrodes 28 which are connected to a field bias source 30. As a result, there is established between the electrodes a constant electric field. The ink drops, which bear charges in accordance with the video signal, enter this field and are deflected by an amount which is proportional to the amplitude of the charge. This enables intelligent writing to occur on a writing medium 32, which is moved at some synchronous rate past the electrodes. Drops which do not bear a video charge are captured by a tube or trough 34 which is judiciously placed at one side so as to capture these drops. It leads to a waste reservoir 36. The paper 32 moves into the plane of the drawing whereby its motion, together with the deflection of the drops, may be used for forming intelligible characters.

In order to write lines of information across a wide sheet of paper, an arrangement such as is schematically represented in FIGURE 2 may be employed. Here, the ink drop writer is attached to a traveling nut 42 which is freed to move on a journally supported lead screw 44. At the top of the ink drop writer is a nut 46 which is free to slide along a rod 48. Accordingly, as the lead screw 44 is rotated in one direction or the other, the ink drop writer will move in a direction dictated by this rotation along a path parallel to the lead screw.

By ink drop writer is meant a housing which supports the ink reservoir 10, tubing 12, transducer 14, nozzle 20, and charging tunnel 24. The video and sync signal sources are placed elsewhere and are connected to the ink drop writer by wires. The function of the deflection electrodes 28 is performed by a pair of spaced plates 41 which extend the path of travel of the ink drop writer and are placed so that the stream of drops pass therethrough on their way to the paper. A trough (not shown) identical to the tube 34 is provided which extends adjacent the bottom plate.

The paper 50 upon which writing is to occur moves in a direction vertical to the direction of the path of motion of the ink drop writer. A motor 52 has a first shaft 54 extending therefrom to a /2 sector gear 56. The motor has a second shaft 58 extending therefrom to a gear box 60, which functions to reverse the direction of rotation of the shaft 58. This reverse motion is communicated through a shaft 62 to another /2 sector gear 64 in which it terminates. The sector gears are cut so that as the motor rotates the sector gear 56 engages a gear 66 attached to one end of the lead screw to rotate the lead screw 44 so that the ink drop writer is moved from left to right. When the ink drop writer reaches the right-hand end of the lead screw, the sector gear 56 is disengaged from the gear 66 and the sector gear 64 engages a gear 68 on the other end of the lead screw. This results in the lead screw being rotated in the opposite direction thereby returning the ink drop writer 40 to its home position on the left-hand side of the lead screw. Motor control apparatus 70 serves the function of energizing the motor to rotate over the interval required for the ink drop writer to make one round trip path along the lead screw. The motor control then waits until it receives a signal from a gate, shown in FIGURE 4, which enables the motor to again function to cause the ink drop writer to make a round trip path.

A sensing switch circuit 72 has a feeler 74 which trips the sensing switch circuit when the ink drop writer returns to the home position. The sensing switch circuit may be any Well known arrangement for generating a signal when the feeler 74 is actuated. This can be, for example, an arrangement for connecting a battery to the terminal 71 until the feeler 74 is out of contact with the ink drop writer.

It should be noted that when the ink drop writer is in the home position the deflection plates 41 are not present.

FIGURE 3 illustrates in partial sectional view and partial schematic view an arrangement, in accordance with this invention, which is provided when the ink drop writer is at the home position. At this time only, the sync signals, which, by way of example, are 66 kHz., are applied to the charging tunnel 24. The sync signals are applied, in accordance with this invention, through a phase changing network 80 to the electromotive transducer 14, which vibrates the nozzle 18. Ink drops 22 are formed within the charging tunnel. A target bar 84 is placed in the path of the drops. Should the drops be charged properly, they give up their charge when they strike the target bar 84. There is a flow of current through a resistor 86 whereby an input voltage is applied to the amplifier 88. This is amplified and applied to an integrator 90. The integrator is used in order to insure that more than an occasional charge drop strikes the target bar 84.

Sensing switch 72 provides an output to a delay circuit 92 which delays this signal long enough for a sampling of the drops being formed to strike the target bar 84 so that the integrator can build up to a sulficient output volt age. This may be an interval for about 20 drops to form. At this time, a phase control network 94, the details of which will be shown in FIGURE 5, in the absence of an integrator signal, causes the phase change network 80 to change the phase of the 66 kc. sync signal being applied to the electromotive transducer 14 by 180. This serves to correct the phase of the formation of the drops so that they receive a proper charge. In the presence of an input to the phase control network from the integrator 90, no change in phase is initiated, since the drops are being properly charged. A catcher 96 is provided for the ink drops after striking the target bar 84.

It has beend found that if the charging signal applied to the charging tunnel is in phase with the drop separation time, each drop will take the proper charge. It has also been found that when every other drop is charged, as by applying a 33 kHz. signal to the charging tunnel, the drops will combine (in the absence of a deflecting field) downstream into drops of twice the mass and half the frequency at which the drops are formed. If the field is not in phase with the drop separation time, the drops Will not gather downstream, leaving the drop frequency unchanged. Since the drops are formed at a 66 kHz. rate, if the phase of the drop formation is proper, then at a downstream collection point the drops are combined and occur at a 33 kHz. rate. Advantage of this phenomenon may be taken to determine whether or not the phasing of the drop formation is proper.

FIGURE 4 illustrates another arrangement in accordance with this invention for detecting and correcting the drop formation phasing. Similarly functioning parts shOWn in previous figures of the drawing have the same reference numerals. There is provided for this embodiment of the invention a frequency divider 17 which divides the output of the 66 kHz. sync signal source by 2 and provides an output 33 kHz. pulses. These are applied to the charging tunnel 24 as video signals, which results in charging every other drop (22A), the remaining drops 22B are not charged. This is so, since drops are still being formed at a 66 kc. rate. The drops travel, as described in connection with FIGURE 3, until they strike a drop detector and phase control circuit 95. It will be noted that the drops, if formed in the proper phase, combine downstream so that a charged and uncharged drop combine and strike the drop detector 95 with a 33 kHz. frequency.

FIGURE 5 represents a circuit arrangement for detecting the proper phasing of ink drop formation by the sensing of the frequency of the drops which are detected. A drop detector such as is illustrated in FIGURE 3 may be employed, since where improper drop charging occurs, instead of alternate drops being charged, with guard drops inbetween, every drop or groups of drops receive some charge. As a result, a voltage is generated across the resistor 86 which has the frequency of the drops which strillie the target bar 84 which frequency will exceed 33 c.

An alternative arrangement for a drop detector, which may be employed, is to use a piezoelectric material body 96, which is located at the position of the target bar 84. This generates a pulse output responsive to every drop which falls upon the pz material. This output has the frequency of the drops falling on the pz material. The result is, in the case of properly phased drops, an output signal at a frequency of 33 kc. If the drops are not properly phased, then the phenomenon previously described, that of a pair of drops consisting of a charge and uncharged drops, forming a single drop, does not occur, and therefore the frequency of the output signal of the pz drop detector is greater than 33 kHz.

The drop detector 96 is followed by a 33 kHz. filter 98, the output of which is applied to an integrator 100. It should be appreciated that the integrator will provide an output signal in the event that the drops are being formed with the proper phase, and will not provide an output signal in the event that the drops are not formed with the proper phase.

The output of the integrator 100 is applied to an inverter 102. A clock generator 104 applies a clock pulse to an AND gate 106. The output of the inverter 102 is also applied to the AND gate. Accordingly, in the absence of an output from the integrator, the AND gate will have its two required inputs, whereby it provides an output which can drive a flip-flop 108 from one to the other of its two stable states. One of its outputs designated Q can enable an AND gate 110 to pass kHz. signals from the source 16 to an OR gate 112. The 6 output of flip-flop 108 is applied to a second AND gate 112. When the 6 output of the flip-flop 108 is high, the AND gate 114 can pass 66 kHz. signals which have been phase shifted 180 by a phase shift network 116. The output of AND gate 114 is a second input to the OR gate 112. The output of the OR gate is used to energize the electromotive transducer.

The circuitry described following the integrator 100 can be used for the phase control network 94 and the phase change network 80 in FIGURE 3.

The output of the 66 kHz. source 16 is also applied to a flip-flop 120 which serves the function of dividing its input by one-half. Thus, the output of flip-flop 120 is a 33 kHz. signal which is applied to an AND gate 122. A second input to AND gate 122 is the signal from the sensing switch 72. Accordingly, when the ink drop writer 40 reaches its home position, AND gate 122 will provide an output of 33 kHz. signals. Only when the ink drop writer is in the home position are these 33 kHz. signals applied to the charging tunnel.

The output of the 66 kHz. signal source 16 is also applied to a delay network 124. This functions to delay its input by one-half the interval required for a 66 kc. pulse. The result is that the 66 kHz. pulse is shifted so that it fits inside of a 33 kHz. pulse. The output of the delay circuit 124 is used to enable an AND gate 126 whose other input is a 33 kHz. pulse output of the AND gate 122. Accordingly, the output of AND gate 126 comprises 33 kc. pulses which have the pulse width of a 66 kc. pulse or, narrowed 33 kHz. pulses. The purpose of this is to insure that the phasing of the charging signal falls in the region wherein the video signal which is to be subsequently applied to the charging tunnel attains its full pulse width, or the region which is between the rise time and fall time of the video pulses.

After the phase of the formation of the ink drops has been checked and the phase of the signal vibrating the nozzle has been corrected, if necessary, the motor control 70 is energized to cause the ink drop writer to make another round trip, at which time the phasing of the ink drop formation is again checked. This is accomplished by delaying the output of the sensing switch 72 by means of a delay circuit 128 over the interval required to accumulate a sufficient sample of ink drops to insure that the proper test has been made.

The output of the delay circuit 128 is applied to an AND gate 130. The other input to the AND gate 130 which is required is an output from the integrator 100. This does not occur until the drops are in proper phase with the 33 kc. signal which is applied to the charging tunnel. The ink drop writer then leaves the home position at which time the application of 33 kc. signals to the charging tunnel is discontinued until it returns back to the home position.

There has been accordingly described and shown herein a rovel and useful arrangement for detecting the phase of formation of the ink drops which are used in the ink drop writing system, and, if proper, correcting the phase of the drop forming signal to insure that the ink drops, which are formed, receive a charge in response to the video signal applied to the charging tunnel.

What is claimed is:

1. In an ink drop writing system of the type wherein ink under pressure is delivered to a nozzle, a transducer vibrates the nozzle, synchronizing signals from a source drive the transducer, the nozzle emits an ink jet which breaks into drops in synchronism with the vibration of the nozzle, a charging tunnel is positioned in the region at which the ink jet breaks down into drops, a video signal source synchronized by sync signals applies its signals to the charging tunnel for charging each drop formed therein, said charged ink drops passing out from the charging tunnel;

the improvement in establishing the phase of formation of said ink drops relative to the occurrence of a video signal on said charging tunnel comprising means for applying a fixed frequency charging signal to said charging tunnel;

detecting means positioned adjacent said charging tunnel for receiving all of said ink drops;

means connected to said detecting means for produc ing an output voltage when the ink drops received by said detecting means are formed in phase with the signals applied to said charging tunnel and for not producing an output voltage when the signals are not formed in phase; and

means responsive to the absence of said output voltage for changing the phase of the sync signals applied to said electromotive transducer to correct the phase of the drops which are formed.

2. In an ink drop writing system as recited in claim 1 wherein said detecting means comprises a conductive rod for collecting the charge from each drop impinging thereon, and said means for generating a signal in response to the drops which impinge on said detecting means being formed with the proper phase comprises meansv for producing a voltage having an amplitude determined by the charges on said drops being collected, and means for integrating said voltage. v

3. An ink drop writing apparatus as recited in claim 1 wherein said detecting means for receiving said ink drops comprises a conductive bar;

said means for generating a signal responsive to the drops detected by said detecting means are formed with the proper phase comprises means for generating a voltage having a frequency determined by the frequency of the occurrence of charged drops which impinge upon said detecting means; and

a filter having a pass frequency equal to one-half of the frequency of drop formation, said filter having its input connected to receive the output of said means for generating a voltage, and an integrator having its input connected to the output of said filter.

4. An ink drop writing apparatus as recited in claim 1. wherein said detecting means comprises means for generating an output voltage responsive to each drop striking said detecting means; A

a filter connected to said detecting means, said filter having a pass frequency determined by one-half of the frequency of drop formation; and

an integrator connected to the output of said filter.

5. Ink drop apparatus including:

a source of ink under pressure;

a nozzle connected to receive ink from said source and to emit a jet of ink;

an electromotive transducer means attached to said nozzle for vibrating said nozzle;

21 source of synchronizing signals;

means for applying signals from said source of synchronizing signals to said electromotive transducer means to cause said electromotive transducer to vibrate said nozzle in response thereto whereby the ink jet which is emitted therefrom breaks into drops having a phase determined by the phase of said synchronizing signals;

a charging tunnel positioned at the region at which said ink jet breaks down into drops;

a source of video signals synchronized by said synchronizing a signal source;

means for applying said video signals to said charging tunnel whereby each drop which is formed within said charging tunnel receives a charge as determined by said video signal;

means for moving said nozzle and charging tunnel from a home position along an axis to a terminal position and back to said home position;

a pair of deflection electrodes positioned adjacent the side of said charging tunnel through which said drops exit, said electrodes extending fro-m a location outside of said home position to said tunnel position and parallel to said axis;

means for applying a fixed bias to said deflection electrodes to establish an electric field through which said drops pass;

means for generating a signal when said nozzle and charging tunnel are at said home position;

means for deriving fixed frequency and phase signals from said synchronizing signal source;

means for applying said fixed frequency and phase signals to said charging tunnel when said charging tunv nel is in the home position;

detecting means positioned adjacent said charging tunnel at said home position to receive drops passing therefrom and to produce an output indicative of the phase of formation of said drops relative to the phase of the fixed frequency and phase signal applied to said charging tunnel; and

means responsive to the output of said drop receiving means for altering the phase of the synchronizing signals applied to said electromotive transducer to change the phase of formation of said drops by said nozzle until the output of said drop receiving means indicates that they have the proper phase.

6. Ink drop apparatus as recited in claim wherein said detecting means comprises a conductive rod for collecting the charge from each drop impinging thereon, and said means for generating a signal in response to the drops which impinge on said detecting means being formed with the proper phase comprises means for producing a voltage having an amplitude determined by the charges on said drops being collected, and means for integrating said voltage.

7. Ink drop apparatus as recited in claim 5 wherein said detecting means comprises a conductive bar;

said means for generating a signal responsive to the drops detected by said detecting means are formed with the proper phase comprising means for generating a voltage having a frequency determined by the frequency of the occurrence of charged drops which impinge upon said detecting means; and

a filter having a pass frequency equal to one-half of the frequency of drop formation, said filter having its input connected to receive the output of said means for generating a voltage, and an integrator having its input connected to the output of said filter.

8. Ink drop apparatus as recited in claim 5 wherein said detecting means comprises means for generating an output voltage responsive to each drop striking said detecting means;

a filter connected to said detecting means, said filter having a pass frequency determined by one-half of the frequency of drop formation; and

an integrator connected to the output of said filter.

9. An ink drop apparatus as recited in claim 5 wherein there is included means for moving said nozzle, electromotive transducer and charging tunnel reciprocally from a home position along a path to an end position and back to the home position, and means for preventing said means for moving from operating until said drop receiving means output is indicative of drop formation having proper phase.

References Cited UNITED STATES PATENTS 3,298,030 1/1967 Lewis et al. 346 3,369,252 2/1968 Adams 34675 3,373,437 3/1968 Sweet et a1. 34675 3,404,221 1 0/1968 Loughren 1785.2

RICHARD B. WILKINSON, Primary Examiner JOSEPH W. HARTARY, Assistant Examiner U.S. Cl. X.R. 1786.6 

